Tanning



Patented Nov. 5, 1940 UNITED STATES- PATENT OFFICE TANNING No'Drawing. Application April 80, i940, Serial No. 332,449

11 Claim.

This invention relates to the production of.

leather. It is more particularly directed to the tanning of skins by subjecting them to an aqueous solution containing a foam depressant and an acidic polymeric material in which the acidity is due to carboxyl groups attached to aliphatic carbon atoms.

The conversion of skins into leather is accompanied by profound changes in their physical characteristics. They become opaque, and a distinct fibrous structure becomes apparent. The stiffness characteristic of dry rawhides disappears to a great extent and they become comparatively flexible. They assume a characteristic attractive appearance and soft feel." Tanning also renders the product imputrescible. For useful tanning these changes must be relatively permanent, and the leather should be resistant to de-tanning by water, at least at ordinary temgg peratures.

The ancient and well-developed art of tanning customarily effects the conversion of skins into leather by the use of vegetable preparations that contain tannins. Vegetable tanning ma- 25 terials, such as quebracho extract, are quite slow in their action, and tanning processes employing them require excessively long periods of time for completion. The leather produced using vegetable tanning materials is characteristically colored, and it is diflicult to obtain good true colors upon dyeing. It is particularly diflicult to produce satisfactory light-colored leather.

Tanning processes employing metal compounds, such as chromium sulfate, are also known. Such processes are, however subject to a number of disadvantages in operation, and the leather produced is characteristically colored. White leather, so-called, can be produced by employing bleaching if required, but this leather is. not truly white since it-has a distinct blue, yellow, green, or gray tint.

Numerous synthetic tanning materials have been proposed, but these are markedly inferior to the vegetable or metal compound tanning agents mentioned. In some instances the leather produced with known synthetic tanning agents is not sufiiciently resistant to de-tanning by water, and in other cases the leather lacks the necessary fullness and plumpness. Therefore, these synthetic tanning materials of the prior art are customarily used in conjunction with a vegetable tanning material or a metal compound tanning agent, and they are useful principally because of properties apart from their characteristics as tanning agents,

Recently there have been developed greatly improved tanning processes involving the use of an acidic polymeric material in which the acidity is due to carboxyl groups attached to aliphatic carbon atoms. These processes produce leather 5 of good color and the leather is additionally of good character, being opaque, soft, full," and flexible.

While these recently developed processes e'mploying an acidic polymeric material may readily l0 and easily be employed by those familiar with the technique of tanning, their use is complicated by the fact that the acidic polymeric materials in aqueous solution tend to build up heavy foams in tanning wheels. Such foams act as w a cushion for the hides during the tanning process and markedly reduce the vigor of the mechanical action of the tanning wheel.

It is an object of this invention to improve these recently developed processes involving the 20 use of an acidic polymeric material. It is a further object to provide processes which are rapid, simple, and easily controlled and which greatly increase the facility of employing the recently developed tanning processes. It is a 25 still further object of this invention to provide tanning processes by means of which there may be produced a very high quality of leather. It is a still further object of this invention to provide processes in which aqueous solutions -of 30 acidic polymeric materials are used as tanning agents without difiiculties due to foaming of the solution. Still further objects will become apparent hereinafter.

These and other objects of my invention are 35 attained by processes comprising adding a foam depressant to an aqueous solution of an acidic polymeric material in which the acidity is due to carboxyl groups attached to aliphatic carbon atoms and tanning skins with such solutions. 0 In a preferred embodiment of the invention the leather is treated with aluminum sulfate or ferric sulfate. Difiiculties due to foaming are substantially avoided by carrying out the processes in the presence of the foam depressant, and the leather produced has excellent general character.

The processes of this invention may be used for the treatment of any type of skin adapted to be converted into leather or fur. It is to be observed that the term skin is used gener- 5o ically to include heavy skins such as cowhide, lighter skins such as goatskin and calfskin, and also skins of fur-bearing animals. It will naturally be necessary to adapt the processes to the type of skin to be treated. For instance, goat- 55 skin may be more rapidly tanned than calfskin, but those skilled in the art are. well aware of such factors and may readily adapt the agents of this invention to the specific needs of particular specialized problems.

Skins to be tanned according tothe processes of this invention may be prepared in any of the manners customary in the art. They may suitably be unhaired, limed. delimed and bated, and pickled. The skins may if desired be depickled. They may also be given a salt liquor treatment to soften them up and to render them of more uniform condition as is the practice in prior art tanning processes.

While skins prepared in any manner may be treated according to the processes of this invention, the pH of the skins is important. As will be observed below, the tanning is eifected at certain conditions of acidity and the skins may tend to change these conditions. The tanning solution may suitably be controlled to compensate for any variance of the pH of the skins from that of the tanning solution. It may sometimes be found advantageous to adapt the processes for preparing the skins so that a skin prepared for tanning is approximately at the pH of the taning solution.

Too rapid reaction of the tanning agent with the skin in the first stages of the process should be avoided in order to prevent surface hardening of the skin. In tanning with acidic polymeric tanning agents this result is accomplished by careful adjustment of the pH of the tanning solution. The exact acidity of the tanning solution may be widely varied depending upon the specific type of skin to be treated and depending upon the specific type of leather to be produced. While a wider range of acidity may be used, it will generally be found desirable to have the tanning solution initially at a pH from about 4.7 to 5.0. Still more specifically, it will be found that under many conditions of operation a pH of about 4.75 is optimum. At a pH much below 4.7 the affinity of skins for the polymerization products becomes so great that surface hardening takes place, while at a pH much above 4.7 the affinity of the hides for the tanning agent is so decreased that penetration is not sufllciently rapid for the best results.

The acidity of the polymerization products may suitably be adjusted by the use of such alkalies as alkali metal hydroxides or carbonates, ammonium hydroxide, and organic bases such as ethanolamines. As has been observed before, the pH of the hide should be considered in adjusting the pH of the tanning solution so that the tanning solution will be employed at an acidity within a desired range. To assist in maintaining the tanning solution at about the optimum acidity a suitable buffer salt such as sodiumacetate or sodium acetate or sodium phosphate may be included in the tanning solution.

After satisfactory penetration of skins by the tanning agent has been effected the rate of tanning may be accelerated by lowering the pH of the solution. The pH to which the solution 1 should be brought to effect complete tanning will vary considerably with the specific type of skin being treated. It will not generally be desirable to go to a pH below about pH 3 since, at a higher hydrogen ion concentration, hydrolysis of the skin may take place. As a practical matter it will be found that the pH should be lowered to about 3.4 to 4.2, while more specifically it be found that in many processes a pH of about 4 will be most satisfactory.

The lowering of the pH of the tanning solution may suitably be effected by the use of any acidic material such as lactic, hydrochloric, sulfuric, acetic, phosphoric, sulfanic, and formic acids.

The considerations as to the type of apparatus to use, the time to be allowed for tanning, the temperatures of tanning, and the amounts of tanning agent are substantially those known to the art in connection with prior art tanning processes. The time allowed for tanning must be sufficient to permit complete penetration of the tanning agent and the pH should not be lowered too rapidly or there may be puckering and apparent over-tannage of the grain surface. The tanning can best be effected at room temperature, say 20 to 0., but temperatures somewhat higher than those used by the art can successfully be employed if desired. The exact amount of the tanning agent to use can best be determined by a few simple tests under the specific conditions of the process selected and with the specific skin to be treated. In general, enough of the tanning agent must be used to effect the tanning desired but unduly large amounts should not be used as they will not be taken up by the leather in a reasonable period of time.

The recently developed tanning agents with which a skin is treated in the presence of a foam depressant according to the processes of my invention are composed of an acidic polymeric material in which the acidity is due to carboxyl groups attached to aliphatic carbon atoms, that is, carbon atoms which are not a part of an aromatic nucleus. It is preferred to use as tanning agents acidic polymers of alpha-unsaturated aliphatic carboxylic acids, while still more specifically, it is preferred to use an acidic polymer of alpha-methacrylic acid.

The expression acidic polymeric material in which the acidity is due to carboxyl groups includes a wide variety of polymers all generically suited for use as tanning agents. Included are not only polymers in which the polymeric structure is built up by synthetic means, but also those in which the polymeric molecule is built up by nature, such as cellulose glycolic acid, alginic acid, and pectic acid. The suitable acidic synthetic polymers include, not only the self-polymers and interpolymers of polymerizable aliphatic carboxylic acids, but also acidic condensation polymers, e. g., those in which an aliphatic polycarboxylic acid, such as citric acid or tricarballylic acid, is reacted with a polyhydric alcohol, such as glycerol.

As already indicated, best tanning results are obtained with polymerization products of alphaunsaturated aliphatic carboxylic acid. Examples of such are the self-polymers of acids of the acrylic series such as polyacrylic acid, polyalphaethylacrylic acid, and polyalpha-methacrylic acid. Still other suitable polymerization products of alpha-unsaturated aliphatic carboxylic acids are the interpolymers of acids of the acrylic series with polymerizable materials, for example, styrene and methyl methacrylate. Mixtures of such polymerization products may of course be used.

The term polymerization products of alphaunsaturated aliphatic carboxylic acids also includes interpolymers of alpha-unsaturated dicarboxylic acids such asmaleic acid or of maleic anhydride, its equivalent, with polymerizable materials such as styrene. Products obtained by interpolymerizing the alpha-unsaturated carboxylic acids with each other such as interpolymers of methacrylic acid with acrylic acid or with maleic anhydride, may be used. There is no particular restriction on the type of added polymerizable material except that it be one which does not destroy the free acidity of the final polymer, to which it is believed the tanning effect is largely attributable.

These recently developed tanningagents are preferably used in aqueous media.- The preferred agents are water-soluble initially, as is polyacrylic acid and polymethacrylic acid, or are capable of being brought into solution with aqueous alkali metal hydroxides, amines, or other bases, as are the interpolymers of maleic anhydride with styrene. For best results the solubility in either instance should be such that the solution may be brought to the proper pH for tanning without precipitation of the taming agent. In some instances, however, agents that are moderately or even only slightly soluble can be used with some degree of success, due possibly to the fact that, as the small amount in solution is used up, a small additional amount of the polymer in turn goes into solution, and so on.

As examples of acidic polymeric materials which may be used for the tanning oi skins there may be mentioned heat-polymerized polymethacrylic acid prepared by heating methacrylic acid with benzoyl peroxide as a catalyst, polyacrylic acid prepared by heating acrylic acid with benzoyl peroxide in toluene, a polymeric polycarboxylic acid which is a hydrolysis product of methylacrylate polymer and is prepared by heating methylacrylate polymer with toluene and adding potassium hydroxide in ethyl alcohol, acrylic acid-methacrylic acid interpolymer prepared by heating acrylic acid with methacrylic acid in toluene with benzoyl peroxide catalyst, and maleic anhydride-styrene interpolymer prepared cautiously heating together equal parts of styrene and maleic anhydride.

As will be apparent from the list of illustrative polymeric materials the acidic polymers suitable for use as tanning agents may be made in a number of ways. The polymerization may be effected by any of several well-known procedures, such as at elevated temperatures with influences the molecular weight of the polymer. As shown by Staudinger, comparatively low temperature reactions tend to produce high molecular weight products whereas high temperatures have the opposite effect. In the work leadin to the present invention it was found that these relationships were correct and that the tanning results vary somewhat with the different types of polymers. For example, when polymerization of acrylic acid was eflected at room temperature by exposure to ultra-violet radiation, the prod uct was a glassy, brittle solid which was difllcult to dissolve in water. This agent tanned only slowly and yielded a product lacking in opacity and fullness. Polymerization in a low-boiling solvent such as acetone, at a temperature of 60 C. or less, also yielded an agent which produced relatively inferior leather. The poorer tanning effect of these high molecular weight polymers may be due to the relatively poorer penetration of the polymer into the skin.

On the other hand, as shown in the examples, polymerization by heating to high temperatures without a solvent or in a high-boiling solvent such as toluene at a temperature above 100 0.,

'yielded' readily water-soluble products which produced good leather. Whereas these superior materials were polymerized to high molecular weight as shown by the fact that they are amorphous solids, their ready solubility in water indicated that they were much lower in molecular weight than the agent produced, for example, by polymerizing acrylic acid at room temperature by means of ultra-violet light.

It is understood that the above applies chiefly to acrylic acid and merely illustrates one of several instances in which somewhat difierent tanning results may be expected with polymers prepared by diflerent methods.

In addition to the polymers above listed, the following polymerization products are also illustrative of polymeric tanning agents suitable for use in the processes of this invention. These are given in tabular form for convenience.

The proportions given in parentheses in the table refer to proportions of the constituents found in the polymers upon analysis; the other figures given under the heading Materials Polymerized indicate the initial proportions of the starting material.

Polymerization products of alpha-unsaturated acids Material polymerized Method oi preparing polymer Appearance of product Solubilitles Alpha-ethyl acrylic acid Mmomer exposed to ultraviolet light for five Opaque white solid Sotllugle is dilute sodium ays. y roxi e. Acrylic acid 75:styrene 25 (82:l8) 15% solution of monomers in toluene at 100- C. White powder Soluble in dilute sodium for 30 mins. with 1% benzoyl peroxide. hydroxide. Allpiha-ethyl acrylic acid83: styrene Mgnomers exposed to ultraviolet light for 4 .do Do.

ays. Methacrylic acid 50:1:naleic anhy- 15% solution oi monomers in toluene at 100 0. do Soluble in water.

dride 50 (92:8). for 14 hrs. with 1.25% benzoyl peroxide. Maleic anhydride 50: methacrylic 15% solution oi monomers at 90-100 0. for 4 hrs. do Soluble in dilute alkali.

acid 25: styrene 25. with 1.25% benzoyl peroxide.

benzoyl peroxide as a catalyst and in the presence of solvent or dispersion media such as acetone, toluene, or water, or by heating in the presence of a solvent and in the presence or absence of a catalyst, or by exposure to ultraviolet light.

Tanning action is afiected to a certain extent by degree of polymerization and the latter in turn, as is well known, by polymerization conditions. It is known, for example, that in the polymerization of acrylic acid the temperature is \t which the reaction is carried out markedly Also illustrative of the broad type of polymeric compound above illustrated are the acidic polymers obtained by partial or complete hydrolysis of polymers of interpolymers of derivatives of alphaunsaturated acids such as the esters, amides, or nitriles. One such polymer, the hydrolyzed methacrylate polymer, is mentioned above.

As has been noted above, one particularly satisfactory group of polymeric tanning agents are the acidic polymerization products of methacrylic acid. Among the tanning agents of this specific group there may be mentioned as illustrative polymethacrylic acid prepared by heating methacrylic acid in water with asmall amount of benzoyl peroxide catalyst, polymethacrylic acid prepared by heating methacrylic acid in toluene with benzoyl peroxide as a catalyst, polymethacrylic acid prepared by exposing methacrylic acid to the action of ultra-violet light, partially hydrolyzed methyl methacrylate prepared by dissolving methyl methacrylate polymer in benzene and heating with potassium hydroxide in absolute alcohol, methacrylic acid-styrene interpolymer prepared by polymerizing five parts of styrene with thirty-five parts of methacrylic acid in toluene with benzoyl peroxide as a catalyst, methacrylic acid-methyl methacrylate interpolymer prepared by dissolving methylated starch in water, adding 87.5 parts of methacrylic acid and 12.5 parts of methyl methacrylate and effecting polymerization in the presence of a small amount of benzoyl peroxide.

In addition to the methacrylic acid polymers listed there is set out in tabular form for convenience a number of still further illustrative tanning agents of this group. All of these polymers, with the exception of the inter polymer of methacrylic acid with methacrylamide, which is a yellowish friable resin, are obtained as white powders of varying degrees of water and alkali of aluminum. The salt selected may be added to the spent tanning liquor containing the foam depressant, and the tanned skins may be agitated in this solution as shown in Example 2 hereinafter.

It will be understood that the acidic polymers may if desired be used together with other tanning agents or tanning assistants in manners known to the art. They may, for instance, be used in conjunction with vegetable tanning materials such as quebracha extract, with chrome tans, or with synthetic tanning agents containing sulfonic acid groups. The tanning assistants used in conjunction with the acidic polymers may be used simultaneously or may precede or follow the treatment with the polymer.

The leather obtained according to the preferred processes of this invention is white but it may if desired be treated with white pigment or may be colored during or after the tanning process by the inclusion of any of the common leather dyes and pigments. The dyeing may be effected during the treatment with a metal salt.

Leather produced according to the processes of this invention may be subjected to any of the various kinds of finishing treatments customarily used. The leather if desired may be solubility. suitably filled or given any of the numerous Methacrylic acid interpolymers m m Proportions v g gg g f Method of preparing interpolymer Solubillties Original By analysis Dieth l iumarate 157 toluene solution of monomers heated at 100 :56 I 83:17 Readll soluble in wet y for 16 hrs. with 1.33% benzoyl peroxide. y er Butadiene 25% solution of monomers in mixture of 14 parts 80:20 Partly soluble in water. Readily of toluene and 1 part carbon tetrachloride solubleindllnte sodium hydroxide. heatgildior 24 hrs. at 65 C. with 1% benzoyl ro e. Vinyl acetate 15 toluene solution of monomers heated at 90- 75:25 83. 5:16. 5 Soluble in water.

. l0 0. for 30 min. with 1.25% benzoyl peroxide. Unsym-dich1orethylene.- 15% toluene solution of monomers heated at 75:25 86:14 Partly soluble in water. Readily 904%; C. for 15-16 hrs. with 1.25% benzoyl solubleindilute sodium hydroxide.

1'0 6. Indene 15$: toluene solution of monomers heated at 87. 5325 94:6 Partly soluble in water. Readily flu-107 O. for 1 hr. with 1.25% benzoyl peroxide. soluble in dilute sodium hydroxide. Vinyl chloride 25% toluene solution of monomers heated in 80:20 Difllcultly soluble in water. Readily autoclave ed. 65 0. for 24 hrs. with 1.0% bensoluble in dilute sodium hydroxide. zoy peron e. 7 Vinyl chloroacetate 25 a benzene solution of monomers heated 26.5 50:50 72:28 Insoluble in water. Soluble in at 65 0. with 0.5% benzoyl roxide. alkali. Methacrylnmide 15% toluene solution of monomers eeted 16 hrs. 75:25 74:26 Diflieultiy solublelnweter. Readily at Oil-100 O. with 1.25% benzoyl peroxide. soluble in dilute sodium hydroxide.

In both columns, the percentage of methacrylic acid is given first.

I have found that when the above-described acidic polymer materials are used in aqueous solutions for tanning skins. the degree to which the skins can be agitated in conventional tanning equipment such as tanning drums'is less than when conventional tanningsolutions are used. I have further found that the vigor of agitation of skins in solutions containing acidic polymeric materials can be remarkably increased by adding to the solutions small amounts of foam depressants. Th penetration of the skins by the tanning ag t is greatly aided by this increased mechanical action, the time required for tanning is thereby decreased, and evenness of tanning is promoted.

After tanning with an acidic polymeric material has been completed, the quality of the leather produced may be improved by treating the leather with a salt of a metal selected from the group consisting of aluminum, iron, titanium copper and chromium. The salt used may be a sulfate, chloride lactate, acetate, nitrate, or sulfamate, but it is preferred to use the sulfate surface treatments customary to the art. As has been observed above, the' alkaline surface sizes such as the alkaline casein finishes commonly used in the art to treat white leather may satitsglfactorily be employed without undue difllcul In order that my invention may be better understood, reference should be had to the following illustrative examples:

Example 1 hydroxide to a pH of 5.2 and the partial sodium salt is then dried. Twelve pounds of this partial sodium salt is dissolved in 108 pounds of water and .05 lb. of octanol is added as a foam depressant. This tanning mixture is then added to the drum and the drum is run for three hours. Examination of the contents of the drum at intervals shows that there is no substantial amount of foam present and that the mechanical action of the drum on the hide is vigorous and of a character recognized to give effective tanning action.

After three hours of such agitation the tanning solution is adjusted to pH 3.5 by adding 10 per cent sulfuric acid at fifteen minute intervals during the course of four hours, with drumming. During this period also, inspection shows that mechanical action of the drum on the skins is unhampered because no substantial amount of foam is present.

After the pH has reached 3.5 it is found that the skins have been completely tanned.

Example 2 A maleic anhydride-styrene interpolymer tanning agent is prepared by mixing 50 grams of maleic anhydride with 50 grams of styrene and dissolving the mixture in 450 grams of xylene. To the solution is added 1 gram of benzoyl peroxide and the solution is then heated to the boiling point. Polymerization is rapid and is largely complete in about one minute. The product is isolated by filtration and dried.

Fifty parts by weight of pickled calfskins (drained pickle weight) is prepared for tanning by drumming for about one-half hour in a solution containing 5 parts of sodium chloride and 3 parts of sodium acetate in 83 parts of water. There is then added 20 parts by weight of a 10 per cent solution of a maleic anhydride-styrene interpolymer which has previously been hydrolyzed by boiling a 10 per cent solution of the polymer with 10 parts of sodium hydroxide per parts of polymer and to which has been added 0.3 per cent of octanol to act as a foam depressant.

The skins are drummed in this maleic anhydride-styrene solution containing a foam depressant for about four hours. During this period inspection shows that there is no substantial amount of foam in the drum and the mechanical action of the drum on the skin is consequently unimpeded. The pH of the solution is then lowered to 3.5 by the addition of 5 per cent sulfuric acid solution at one-quarter hour intervals over a period of four hours. Inspection of the skins at this point shows that they are completely tanned.

To improve the quality of the leather produced from the skins tanned by the above procedure, an alum after-treatment is applied. Two parts by weight of aluminum sulfate, A12(SO4)3.18H2O. is added to the/spent tan liquor, in which the octanol originally added remains present. The skins are drummed three-quarters of an hour in this solution and then neutralized with sodium bicarbonate additions in small proportions at one-quarter hour intervals until the pH has been raised to 4.7. The total time required for this neutralization is about 3 hours.

After the alum treatment the skins are removed from the solution, washed, fatliquored with a neats-foot oil-sulfonated oil mixture and dried in the usual manner. The dried leather is found to be of excellent quality.

5 Example 3 A tanning agent is prepared by dissolving 20 parts of maleic anhydride and 20 parts of'vinyl isobutyl ether in 170 parts of toluene and then adding 1 part of benzoyl peroxide. After heating the solution to the boiling point, polymerization begins and proceeds vigorously. After the reaction mixture is cool the product is isolated and dried. Thirty-five parts of tanning material is obtained.

A quantity of calfskins is prepared for tannage by drumming 63 parts (drained pickle weight) of the cafslkin for one-half hour in a solution containing 4.65 parts of sodium acetate and 4.65 parts of sodium chloride in 93 parts of water. Tannage of the skins is then effected by adding 15.4 parts of a 10per cent solution of the above described tanning agent containing as a foam depressant 0.3 per cent of a mixture of primary and secondary branch chain alcohols having 14 to 15 carbon atoms and a boiling point of approximately 200 C. This mixture of alcohols is representative. of mixtures produced by the catalytic high pressure hydrogenation of carbon monoxide.

Following the addition of the tanning solution containing the foam depressant, the skins are drummed for one-quarter hour, after which additional 15.4 part portions of the tanning solution are added with drumming until a total of 4 portions have been added. After the last addition the skins are drummed for 4 hours. During this time inspection shows that the action of the drum on the skins is not impeded by the presence of any substantial amounts of foam.

To complete the tannage, the solution is then acidified to pH 3.5 by adding successive portions of 5 per cent sulfuric acid solution and drumming after each addition, the total time required for the additions being 4 hours.

It is found that skins tanned in the above manner in the presence of a foam depressant are of uniform, even quality, being thoroughly struck through by the tanning agent.

In the foregoing examples I have described my invention with relation to certain specific embodiments thereof, but the particular embodiments shown are not to be construed as limiting the invention. Those skilled in the art will recognize that my invention has a wide range of applicability and that numerous variations and modifications can be made in the particular conditions already described.

As foam depressants I have, for instance, shown octanol and a mixture of higher alcohols obtained from the high temperature and pressure catalytic hydrogenation of carbon monoxide, but it will be understood that other foam depressants may be used. The art is already familiar with various agents which can be used for the purposev of reducing foam formation in aqueous solutions, and I may employ any of these in my novel tanning processes and compositions. I may use, for instance, a foam depressant selected from the group consisting of octanol, lauryl alcohol, alpha-terpineol, cetyl alcohol, and mixtures of high molecular weight branch chain alcohols having 14 to 15 carbon atoms obtained by the high-pressure catalytic hydrogenationof carbon monoxide and having a boiling point above about C. The foam depressant selected should be one which is at least partially soluble in water and which will not react with cats the tanning procedure.

The amount of a foam depressant which I may employ in the processes and compositions of my invention can be widely varied. The amount of a particular foam depressant to employ can readily be determined by adding small amounts thereof to a tanning drum during the course of the tanning operation until enough. has been added to break any foam present. With the higher alcohols already mentioned I have found that amounts up to about 5 per cent based on the weight of the tanning agent will ordinarily sumce. With octanol in particular I prefer to use about 3 per cent based on the weight of the tanning agent.

My novel tanning compositions may be offered to the trade as mixtures of a foam depressant with a tanning agent of the class described. Such mixtures may comprise an admixture of the foam depressant with the dry solid polymeric tanning agent or a solution of the foam depressant and tanning agent. I have found a preferable form to comprise a 25 per cent aqueous solution of the polymeric material containing up to about 10 per cent of foam depressant based on the weight of the polymeric material. More particularly, I have found that a composition excellently suited for use in tanneries comprises a hydrolyzed partially neutralized styrene-maleic anhydride copolymer and octanol as a foam depressant, the octanol being present in an amount equal to about 3 per cent by weight of the copolymer, the tanning composition having a pH of about 5.2.

While I have shown certain specific tanning compositions containing foam depressants in conjunction with acidic polymeric tanning agents and certain specific processes, it will be understood that one skilled in the art may readily employ numerous processes and related compositions without departing from the spirit of this invention.

I claim:

1. In a process for the tanning of skins, the step comprising subjecting a sldn to the action of an acidic polymeric material in which the acidity is due to carboxyl groups attached to aliphatic carbon atoms, the said step being effected in the presence of a foam depressant.

2. In a process for the tanning of skins, the step comprising subjecting a skin to the action of a polymerization product of an alpha-unsaturated aliphatic carboxylic acid, the said step being effected in the presence of a foam depressant.

3. In a process for the tanning of skins, the step comprising subjecting a skin to the action of a polymerization product of maleic anhydride and styrene, the said step being effected in the presence of a foam depressant.

4. In a process for the tanning of skins, the step comprising subjecting a skin to the action of an acidic polymeric material in which the acidity is due to carboxyl groups attached to ali-. phatic carbon atoms, the said step being effected in the presence of a foam depressant selected from the group consisting of octanol. lauryl alcohol, alpha-terpineol, cetyl alcohol, and mixtures of high molecular weight branch. chain alcohols having 14 to 15 carbon atoms and a boiling point above about 150 C. obtained by the high pressure catalytic hydrogenation of carbon monoxide.

5. In a process for the tanning of skins, the step comprising subjecting a skin to the action of an aqueous solution of a hydrolyzed partially neutralized styrene-maleic anhydride co-polymer at a pH of about 4.8 to 5.7 and increasing the acidity of the solution while agitating it, to-

gether with the skin, in the presence of an amount of octanol equal to about 3 per cent of the weight of the co-polymer.

6. In a process for the tanning of skins, the step comprising subjecting a skin to the action of an aqueous solution of a hydrolyzed partially neutralized styrene-maleic anhydride co-polymet at a pH of about 4.8 to 5.7 and increasing the acidity of the solution while agitating it, together with the skin, in the presence of an amount of octanol equal to about 3 per cent of the weight of the co-polymer and then adding aluminum sulfate to the solution and raising its pH.

7. A tanning composition comprising a foam depressant and an acidic polymeric material in which the acidity is due to carboxyl groups attached to aliphatic carbon atoms.

8. A tanning composition comprising a foam depressant and a polymerization product of an alpha-unsaturated aliphatic carboxylic acid.

9. A tanning composition comprising a foam depressant and a polymerization product of maleic anhydride and styrene.

10. A tanning composition comprising an acidic polymeric material in which the acidity is due to carboxyl groups attached to aliphatic carbon atoms and a foam depressant selected from the group consisting of octanol, lauryl alcohol, alpha-terpineol, and mixtures of high molecular weight branch chain alcohols having 14 to 15 carbon atoms and a boiling point above about 150 C. obtained by the high pressure high temperature catalytic hydrogenation of carbon monoxide. 50

11C A tanning composition comprising a hydrolyzed and partially neutralized styrene-maleic anhydride co-polymer and octanol, the octanol being present in an amount equal to about 3 per cent by weight of the co-polymer, and the tanning composition upon dissolving in water forming a tanning solution with a pH of about JOSEPH S. KIRK. 

